A fixing device mounted on an image forming apparatus typically employs a lamp that emits infrared rays, such as a halogen lamp, or an induction heating unit that generates heat by electromagnetic induction as a heat source for fixing an image to imaging medium.
In general, the fixing device includes a pair of a heating rollers (or a fixing belt stretched around a plurality of rollers) and a press roller. In such a fixing device, it is preferable that heat capacity of elements of the fixing device be reduced as much as possible and that only a region that contributes to fixing the image is heated, so that thermal efficiency of the fixing device is maximized.